This invention relates to permeable structures containing microporous sorbent particulate bonded with a polymeric binder. In another aspect this invention relates to respirators, such as protective face or gas masks, containing a permeable bed or sheet comprising bonded, microporous, adsorbent particulate. In a still further aspect, this invention relates to pressure-sensitive adhesive (PSA) polymer and particulates or beads thereof and to methods of making and using the PSA.
Many useful products and processes employ active or functional particulate materials that interact with fluids by sorbing (adsorbing or absorbing) components from the fluids. Examples of such products are worker respirators containing microporous sorbents that purify workplace breathing air; other examples are water purification systems, catalyst systems, drug delivery systems, and ion exchange resins.
Activated carbon, an active or functional particulate having sorptive properties, is widely used to filter air to protect persons against a variety of toxic or noxious vapors, including war gases, industrial chemicals, solvents, and odorous compounds. The activated carbon is derived, for example, from coal or coconut shells and can be produced in the form of powders, granules, and shaped products. It is employed in individual canisters or pads, as in gas masks. Important properties of commercial activated carbon products include those related to their particle size as well as their pore structure. (Kirk-Othmer Encyclopedia of Chemical Technology, Fourth Ed., John E. Wiley and Sons, 1992, Vol. 4, xe2x80x9cActivated Carbon,xe2x80x9d p. 1015-1037.)
The U.S. Occupational Safety and Health Administration has promulgated xe2x80x9cEleven Commandmentsxe2x80x9d on respirator use for workers who may be exposed to workplace hazards (see 29 Code of Federal Regulations, Part 1910. 134 (b), Requirements of a minimal respirator program). Some commercial respirator products approved under such requirements are described, for example, in product bulletins 70-0701-5436-7(535)BE and 70-0701-5436-7(675)11 of the 3M Company and H/S 5666 8/93 of Scott Aviation Company.
U.S. Pat. No. 5,078,132 (Braun et al.) describes a respirator having a porous bonded structure that contains spaced adsorbent granules, that are bonded to one another by certain adherent binder particles, including those of polyurethane. U.S. Pat. No. 4,061,807 (Shaler et al.) and U.S. Pat. No. 4,664,683 (Degen et al.), cited as references in U.S. Pat. No. 5,078,132, describe self-sustaining or self-supporting porous adsorbent bodies or structures made from a mixture of adsorbent granules or particles, such as activated carbon, bonded together or immobilized by certain particulate organic polymer binder, such as acrylics.
In addition to activated carbon, there are other porous sorbent structures that are useful for separating components in gas and liquid streams or for purifying such streams. Examples of other porous sorbent structures include silica gel (a material that appears first to have been developed during the First World War for use in gas masks) and activated alumina (which proved to be superior to silica gel in such gas masks). Other sorbents are the crystalline aluminosilicates or zeolites and molecular sieve adsorbents (formed into macroporous pellets). (Ruthven, D. M., Principles of Adsorption and Adsorption Processes, John Wiley and Sons, 1984, pp. 1-28.)
In many industrial adsorption processes the adsorbent is contacted by the fluid phase in a packed column. Such variables as the particle size, fluid velocity, and bed dimensions affect pressure drop and have an important impact on the processes"" economics. (Ruthven, supra, p 206.)
Active particles also have been incorporated into fabrics to produce sheets containing the particles. U.S. Pat. No. 3,971,373 (Braun) describes a self-supporting, durable, flexible, conformable, low-pressure-drop, porous, sheet product comprising a web of melt-blown microfibers loaded with particles, such as activated carbon particles. U.S. Pat. Nos. 4,433,024 (Eian), and 4,868,032 (Eian et al.) describe fibrous webs of melt-blown fibers and sorbent particles dispersed therein. U.S. Pat. No. 4,677,019 (von Blxc3xccher) describes a process where an aqueous suspension of particlesxe2x80x94e.g., activated carbon, and liquid polymer binder such as polyurethanes, polyacrylates, or elastomersxe2x80x94is sprayed onto a carrier fabric and dried. U.S. Pat. No. 4,904,343 (Giglia et al.) describes a wet-laid process in which a water suspension of activated carbon particles and fibrillated acrylic fibers are used to make a permeable fabric. Other examples of articles using active particles are described in U.S. Pat. Nos. 5,124,177 (Kasmark, Jr. et al.), U.S. Pat. No. 4,510,193 (Blxc3xccher et al.) and 4,296,166 (Ogino).
U.S. Pat. No. 4,000,236 Redfarn et al.) describes a method of forming a conglomerated, bonded, and preferably molded mass of particles of activated carbon bonded together by a polymer, e.g., a water soluble hydroxy propyl methyl cellulose or water insoluble polyvinyl formal. The polymer is rendered adhesive by permeating a random and loose mass of the carbon particles with a solvent (e.g., water) that is subsequently drained off.
U.S. Pat. No. 4,220,553 (Krause) describes a method of producing a porous block for filtering and drying refrigerant fluids. The method involves molding into a block a mixture of solutions of phenolic resin binder and polyurethane resin binder and an activated adsorbent, passing an alkaline gas through the block to cure the resins, purging the gas by passing air through the block, and heating the block to drive off solvents for the binders.
Small polymeric particles suspended in an aqueous medium can be prepared by suspension polymerization. (Kirk-Othmer Encyclopedia of Chemical Technology, Third Edition, John Wiley and Sons, Inc., 1982, Vol. 18, pp. 742-743.) The particles produced by suspension polymerization are generally on the order of approximately 0.1-1 mm in diameter. U.S. Pat. No. 3,691,140 (Silver), U.S. Pat. No. 4,166,152 (Baker et al.), U.S. Pat. No. 4,786,696 (Bohnel), U.S. Pat. No. 5,045,569 (Delgado), 4,833,179 (Young et al.), U.S. Pat. No. 4,952,650 (Young et al.), U.S. Pat. No. 5,292,844 (Young et al.), and U.S. Pat. No. 5,374,698 (Young et al.) and published PCT patent application W094/13751 describe particles of inherently tacky or pressure-sensitive adhesive acrylate polymer produced by a suspension polymerization process.
This invention, in one aspect, provides a permeable, self-supporting, shaped structure that can be usedxe2x80x94for example, as a filter, mask, or respirator for filtration of gases or vapors, such as airxe2x80x94to remove undesired gaseous components therefrom. The structure comprises a mass or agglomeration of active (or functional) particulatexe2x80x94for example, sorbents such as activated carbon, silica gel, or alumina granulesxe2x80x94bonded together with pressure-sensitive adhesive polymer microparticulate distributed in the mass of active particulate. Because the bonding is effected between particulates, namely, the active particulate and the adhesive microparticulate, the bonding is in the nature of spot bonding or point contact where the surfaces of the two particulates are very close to touching or contacting one another at spots or points rather than the bonding being a coating of adhesive on the active particulate. Thus, the surfaces of the bonded active particulate are significantly or essentially exposed or free of bonding adhesive particulate, and the exposed surfaces define most or essentially all of the open interstices in the composite structure that render it permeable. And the bonded structure is flexible (rather than rigid) and thus conformable, due to the viscoelastic or elastic nature of the bonding agent, that is, the PSA polymer. The PSA polymer microparticulate is preferably smaller in size than the active particulate and is preferably distributed or dispersed amongst the active particulate in a small amount sufficient to adhere them together in a unified, flexible, self-supporting, permeable, microporous, composite structure.
A preferred embodiment of the permeable structure of this invention is in the form of a flexible sheet comprising, consisting, or consisting essentially of an agglomeration of a mass of porous adsorbent granules, such as activated carbon or alumina, bonded together by solid PSA polymer microparticulate, such as pressure-sensitive adhesive, polyacrylate polymer, solid micro-beads, which can be in the shape of spheres. The flexible sheet can be formed into a folded or conformable cup-like shape that can be interposed between open or porous, nonwoven or woven, fibrous sheets and the assembly thus adapted to fit over the mouth and nose of a person and used, for example, as a half-mask filtering means or respirator for purifying workplace breathing air contaminated with gaseous hazardous or toxic substances, for example, benzene or toluene solvents. The flexible sheet also can be laminated to a reinforcing sheet, for example, a scrim of an open woven or nonwoven fabric, such as cheesecloth.
In another aspect, the invention includes a canister-type protective respirator that comprises, as the air-purifying filter, the above-described permeable structure in cylindrical, disc, or other shaped form, to provide respiratory protection for workers in workplaces containing hazardous gases or vapors.
In another aspect of this invention, a method of making a permeable structure is provided, where the method comprises the steps of mixing active particulate with PSA polymer microparticulate (preferably an aqueous dispersion thereof) and shaping (e.g., by molding the resulting mixture) and bonding (e.g., by heating or drying) the mixed particulates in a desired form, such as in sheet form for use as a half-mask respirator or in a cylindrical, disc, or other form for insertion into the canister of an air-purifying respirator, or for use as a filter in an air-purifying means such as a room or space air-purifier, or as an oil sorbent means in the form of rovings or booms used to clean up oil spills.
In another aspect, this invention provides a method of purifying a fluid to remove undesired components. The method comprises passing the fluid through the above-described permeable composite structure.
In a further aspect, this invention provides novel PSA acrylate polymer, or polyacrylate product, and microparticulate thereof, for example, in the form of beads, that are useful, for example, to bond particulate, such as microporous adsorbent, to form permeable, shaped structures thereof, and to methods of making and using said PSA polymer product, microparticulate, and dispersions. The novel polyacrylate polymer product comprises (a) suspension stabilizer modifier having a metal cation and (b) a copolymer having repeating units derived from acrylic acid ester of non-tertiary alcohol having 1 to 14 carbon atoms, polar monomer, and at least one of the following copolymerizable components: higher vinyl ester (such as vinyl neo-alkyl ester), styrene sulfonate salt, multi-vinyl monomer, and alkylene polyalkoxy sulfate. Also provided are PSA microparticulate or micro-beads (and aqueous suspensions thereof) of very fine size, namely, 1 to 100 xcexcm, preferably 5 to 50 xcexcm, of the novel polyacrylate, and methods of making such microparticulate or beads by suspension polymerization of the monomers and copolymerizable components.